1. Field of the Invention
This invention relates to an optical communication apparatus, and more particularly to an optical communication apparatus having a base to which optoelectronic semiconductor elements and a wavelength division multi/demultiplexer are accurately fixed.
2. Description of the Prior Art
Optical communication systems using optical fibers have been increasingly applied to wider fields. According to such circumstances, the optical circuit components for use in such an optical communication system are required to be compact in size, and low in production cost. For example, a wavelength division multi/demultiplexer module is generally used for a wavelength multiplex transmission system. Such module incorporates opto-semiconductor elements such as semiconductor lasers, light emitting diodes and photodiodes. Further, the module incorporates a wavelength division multi/demultipIexer provided with multilayered films, and optical fibers. These components are united, and accurately fixed to a base made of glass or ceramic. The thus constituted module can achieve compactness and lower production cost as compared to a discrete configuration.
FIGS. 7a and 7b show a conventional optical wave synthesizer/analyzer module. In FIG. 7a, the module incorporates a light-emitting diode (LED) 51, a photo-diode 52, an optical fiber 53, and an optical wave synthesizer/analyzer prism 56 provided with dielectric film-multilayered filters 55 adhering thereto. Further, the module incorporates optical lenses 54a, 54b and 54c. All the components are accurately fixed by soldering to a ceramic base 57. The ceramic base 57 is disposed on a printed circuit board 62. Further, an LED (light-emitting diode) driver circuit element 63 and a signal processing circuit element 64 are disposed on the printed circuit board 62 in the vicinity of the base 57. The respective terminals (not shown) of the circuit elements 63 and 64 are connected through printed lines to electrode pads 61a, 61b, 61c and 61d formed on the printed circuit board 62. The leads 58a and 58b of the LED 51 and the leads 59a and 59b of the photo-diode 52 are respectively connected by soldering to the electrode pads 61 a, 61b, 61c and 61d.
In this configuration, the leads 58a and 58b of the LED 51 and the leads 59a and 59b of the photo-diode 52 are directly connected by soldering to the electrode pads 61a and 61b and the electrode pads 61c and 61d, respectively. Thus, during the connection, external forces are acted on the LED 51 and the photo-diode 52. As a result, the prescribed positional relationship between the optical components are inevitably changed due to the plastic deformation of the solder used for connection. Further, thermal stress occurs on the solder due to the difference of the thermal expansion coefficients between the base 57 and the printed circuit board 62. Such thermal stress accelerates the creep of the solder, and causes the shift in the positional relationship between the optical components. As a result, the reliability of the conventional optical module is significantly deteriorated.
In the above-described configuration, the optical wave synthesizer/analyzer module is accurately fixed to the flat base. However, there has been disclosed another technique in which optical components are accurately positioned at the prescribed positions on the surface of a photosensitive glass base. FIG. 8 shows an optical circuit component manufactured by use of a conventional technique. In FIG. 8, a photosensitive glass base 69 has the prescribed grooves 65, 66 and 67 formed by accurate etching processes. Packages 52, 53 and 54, and a wavelength division multi/demultiplexer prism 56 are positioned respectively in the grooves 65, 66, 67 and 68, and then accurately fixed to the base 69 by means of soldering. The package 52 incorporates a combination of optical fibers and lenses. The packages 53 and 54 each contain opto-semiconductor elements associated with the lenses. In this configuration, the respective optical components can be positioned in a prescribed arrangement with substantially no need for additional adjustments. Thus, this technique has advantages such that optical circuit components can be manufactured at relatively lower costs.
However, such conventional technique of soldering optical components to a photosensitive glass base still has problems in terms of work efficiency and productivity. Specifically, the soldering portions of the photosensitive glass base may be only etched, or for better quality, a thermal process may be added thereafter to produce a ceramic state. Thus, the types of solder that can be applied to this technique are limited to solders used for ceramic bonding. As a result, there is little flexibility in variation of the solder melting point. Further, ultrasonic oscillation must be additionally applied to achieve satisfactory soldering. Therefore, the work efficiency of assembling optical components becomes lower. Thus, the productivity of manufacturing the optical communication module inevitably becomes lower.
FIG. 9 shows an optical circuit component manufactured by use of a conventional technique. In FIG. 9, a photosensitive glass base 69 has the prescribed groves thereon formed by accurate etching processes. A package 53 that incorporates opto-semiconductor elements and lenses is accurately fixed to the base 69. Specifically, in this configuration, the package 53 can be attached to one of the grooves of the base 69 with substantially no need for additional adjustments. Thus, this technique has been applied to manufacturing processes of optical components such as an optical brancher/coupler and a wavelength division multi/demultiplexer.
However, in the conventional configuration, when the package 53 incorporates an element which generates heat, such as a semiconductor laser, a structural problem in heat radiation arises. Specifically, in FIG. 9, one end of a heat-radiating member 70 is attached directly to the package 53. The other end of the member 70 is attached to a heat sink 71. In this configuration, stress occurs with respect to the base 69 and the package 53 when the member 70 is fixed to the heat sink 71. Moreover, the elasticity of the member 70 causes additional stress with respect to the base 69 and the package 53. The stresses may cause the package 53 to deteriorate in optical and mechanical characteristics, such as by deviation of the optical axis, or other damage.